Ribosomal ribonucleic acid similarities in the classification of Rhodococcus and related taxa

Duplexes were prepared between 14C-labelled rRNA from both Rhodococcus equi C7 and Rhodococcus rhodochrous N54 and DNA from 16 actinomycetes representing the genera Rhodococcus, Mycobacterium, Nocardia, Saccharopolyspora and Streptomyces. The relationships between the organisms were determined by plotting the temperature at which 50% of the duplex was denatured (Tm(e)) against the percentage of rRNA binding (microgram 14C-labelled rRNA duplexed per 100 micrograms filter-bound DNA). All of the strains formed stable duplexes but each organism occupied a definite area on the rRNA similarity map. All of the organisms share a close phylogenetic relationship but representatives of the genera Rhodococcus, Mycobacterium, Nocardia and Streptomyces fell into four recognizable clusters on the similarity map. These data support and extend current trends in the classification of Rhodococcus and allied taxa. The guanine plus cytosine content of the DNA from the test strains was within the range 69.3 to 76.9 mol %.